The invention concerns a heat exchanger, in particular a scraping cooling apparatus for fluid matter which tends to adhere to the heat exchanging surface. The apparatus has a pot-like casing, sealed by an end-plate, and has concentrically interchanging heat-exchanging parts with heat-exchanging agent flowing through. At least three annular chambers are provided for processed matter to pass through, and a power-driven stripping device, consisting of stripping branches that protrude axially and unsupported into the annular chambers for matter with scraper bands fitting closely to the heat-exchanging surfaces, is arranged so as to rotate around the axis of the casing.
For the efficiency of heat-exchangers it is of vital importance that the value of heat transfer at the heat-exchanging surfaces should not or at least not significantly change during operation. Of course, one can select the heat-exchanging agent, the cooling or heating agents and the material for the heat-transfer partitions, the surfaces of which can be modelled accordingly, in such a way that this stipulation is largely accomplished on one side of the partition wall. On the side of the fluid matter this possibility, however, only limited. Firstly, the construction engineer does not definitely know which matter will be put through eventually, and secondly, it is not possible, with all the technical devices available, to prevent the adherence of diverse agents on the heat-exchanging surface. For example, many of the materials are used to change their viscosity when cooling, and the thickening material adheres more easily to the heat-exchanging surface forming an insulating layer which reduces the amount of heat transfer and the resulting degree of efficiency. Other materials precipitate during the heating process. In order to remedy this, scraping devices have been developed which constantly and automatically scrape the heat-exchanging surface on the side conducting the fluid matter.
A scraping cooling apparatus with an elongated tubular double-shell casing through which the heat-exchanging agent flows and along whose inner surface the treated matter is conducted, is known in the art. In this inner chamber there is in the axis of the casing, a shaft that is continually driven during the cooling operation and carries several scraping elements which scrape off the matter adhering to the inner heat-exchanging surface, so that the amount of heat transfer remains largely unchanged.
This construction, however, has a number of disadvantages. The loss of heat is comparatively great due to the fact that the outer surface of the double-shell body is larger than the inner heat-exchanging surface. This tubular model results in a cumbersome construction requiring too much space. Also cleaning is difficult, time-wasting and can often not be sufficiently accomplished.
The loss of heat is lower than in any other existing heat-exchanger, where three additional cylindrical heat-exchanging elements have been provided concentrically within a cooling jacket. Thereby the matter to be treated flows within the body from the chamber, at one face, to the other one on parallel paths between neighboring heat-exchanging parts. As a result, the whole heat-exchanging circuit is relatively short and this lessens the degree of efficiency. Moreover, the matter in the parallel connection strives towards the least resistance, and will therefore flow primarily in the inner annular chamber. The matter, therefore, will be cooled diversely, and the different currents must merge once again before a uniform quality can be achieved.
Accordingly, it is an object of the present invention to improve the degree of efficiency of the conventional heat exchanger.
Another object of the present invention is to provide a heat exchanger of the foregoing character which is simple in construction and may be economically fabricated.
A further object of the present invention is to provide a heat exchanger, as described, which may be readily maintained in service, and has a substantially long operating life.